In mobile communication systems, after a mobile station is switched on, to receive a signal from a base station, the mobile station needs to synchronize timing to receive the signal transmitted from the base station. To synchronize timing, first, the mobile station performs symbol synchronization for the signal transmitted from the base station. Here, symbol synchronization means detecting the timing at which the data symbol is transmitted in the received signal.
FIG. 1 illustrates a format of a transmission signal from a base station. Further, FIG. 1 illustrates a state where a guard interval (hereinafter simply “GI”) is inserted in an OFDM (Orthogonal Frequency Division Multiplexing) scheme or in a single carrier scheme. In symbol synchronization processing, characteristics of GI are used to detect the symbol timing of a transmitted signal. That is, the GI copies a part of the last part of symbol and attaches the copied symbol to the head of the symbol, so that it is possible to perform symbol synchronization by operating an autocorrelation detecting circuit in the receiver.
The autocorrelation detecting circuit detects as an autocorrelation value the value estimated by multiplexing a received signal with a signal delayed by the symbol length τd of data symbol. As shown in the result of autocorrelation detection of FIG. 2, the autocorrelation detecting circuit detects peaks of the autocorrelation value in a cycle of Is (τd+GI length). By this means, the mobile station can detect the symbol timing.
By the way, Patent Document 1 discloses such a technique of controlling the GI length. To be more specific, Patent Document 1 discloses a technique of controlling the GI length such that the maximum delay time of delay waves is short and consequently the GI length is made shorter in a mobile station near the base station, and that the maximum delay time of delay waves is long and consequently the GI length is made longer in a mobile station far from the base station.    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-150850